By next year, beer bought in the U.S. may be more likely to come from a single company than from all the rest combined. That could be bad news for America’s beer drinkers — potentially higher prices for some of the U.S.’s most popular brews and possibly even fewer mainstream brands — if regulatory agencies don’t get involved first.

Last week, Belgium-based beverage conglomerate Anheuser-Busch InBev announced plans to buy Grupo Modelo, the Mexican brewer behind Corona, Pacifico, Negra Modelo and nine other beer brands. For several years AB InBev has owned a 50% stake in the brewer but is now buying up the other half, an acquisition the beer conglomerate has been eyeing for several years.

AB InBev has already cornered 47.7% of the market, a figure that is proudly highlighted on Anheuser-Busch’s home page, and the $20 billion buyout of Grupo Modelo, which has an estimated 6% of the U.S. market, would push AB InBev’s share to well over half of all U.S. beer sales.

That’s why Grupo Modelo is selling its 50% stake in Crown Imports – which exports and markets the Corona brands to the U.S. – to Constellation Brands. The move is designed to prevent antitrust challenges to the AB InBev-Grupo Modelo acquisition. But that move may not be enough to assuage claims of a U.S. beer monopoly.

“In Mexico, they shouldn’t have any issues approving the deal,” says BTG Pactual analyst Rafael Shin. “But in the U.S., it will be a different story.” The move is set to be finalized early next year.

Belgium-based InBev emerged into U.S. beer-drinkers’ consciousness around 2008, when it bought the all-American of American breweries – Anheuser Busch, the St. Louis-based maker of Budweiser and Bud Light.

For the average American beer drinker, the growth of InBev could be bad news. Competition within the beer industry is slowly eroding, and anytime there’s less competition, higher prices are likely to follow.

AB InBev could also decide that it ultimately wants to own fewer brands so it can reduce its marketing costs, and that could give customers fewer mainstream beer options.

The Crown Imports divestiture will help AB InBev make the case that it isn’t cornering all sectors of the market, but if regulatory agencies try to block the deal, it could decide to sell off one or more of its brands.

AB InBev has even attempted to acquire some microbreweries, like its acquisition of Chicago-based Goose Island Beer Co. last year. Even though craft breweries have exploded in popularity over the last several years, they only account for about 6% of U.S. beer sales by volume and 9% by dollars – and are unlikely to ever challenge AB InBev’s dominance in the U.S.